| Knee joint is the largest and very important joint in the human body,and it is easy to damage because of using frequently and bearing large amount of exercise and high stress.The damage of articular cartilage in surface is common in clinic.Due to the particularity of articular cartilage,combined with the poor ability to regenerate itself,its repair treatment is not easy,and one of the reasons is that damage mechanism of the cartilage itself is very complex.Therefore,it is particularly important to further study the pathological and damage evolution mechanism of cartilage.Because it is not easy to measure mechanical response of defect cartilage in the body,and besides we consider the complexity of cartilage injuries.Based on the experiment,this paper mainly study the damage evolution process of micro-defect cartilage with the finite element method,and the regularity of damage evolution and damage mechanics of the cartilage are obtained under various load conditions.These results are conducive to understand the mechanics mechanism of articular cartilage damage.It will provide a reference and theoretical basis for the treatment of cartilage diseases.In this paper,the research process includes numerical simulation research and experimental research.In experimental study,the cartilage specimen of pig knee joint was loaded with the special loading device designed by research group,and experimental images were analyzed with digital image speckle technology.Through comparing the results of simulation and experiment,we found that both trends were similar and it verified the validity of the model.Numerical simulation is the core content of this paper,and cartilage model is established to study the damage mechanism of cartilage with the finite element software ANSYS12.0.Firstly,the fiber-reinforced two-dimensional model was established under a variety of load,which first adopted cross arch fiber structure was closer to the actual.Based on these models,we studied respectively the damage mechanics mechanism of micro-defect cartilage under multiple loads,mainly includes: According to the result of calculation data and damage criterion,the damage evolution process of micro-defect cartilage was analyzed under rolling,sliding pressure and uniform compression,explored the change rule of damage in the direction and velocity,and the impact on damage extension under different rolling or sliding speed and different amount of compression.Besides,the impact of fiber unidirectional damage to the bearing and the impact of internal cracks to the stress distribution of cartilage were also analyzed.Numerical study shows that the damage evolution process of cartilage is more complex than common composite material and it is the result of joint action of many factors such as load form,load size and speed,etc.The damage evolution process of cartilage has a close relationship with the distribution of fiber.In the early period of damage extension,cracks and damage in cartilage spread preferentially along the fiber tangent direction,and fibers played a guiding role in damage process.Complete dense fiber network plays an important role in cartilage,once the fiber fracture will accelerate the damage of cartilage matrix.Compared with sliding compress load,the influence of cartilage damage evolution is bigger under the rolling compress load.In the process of cartilage damage evolution,its extension direction and expansion velocity vary constantly with the damage degree.Under uniform compression,cartilage also extended to deep and both sides.The damage of cartilage and the amount of load compression were obvious positive correlation,and speed has a greater effect on cartilage matrix.Internal crack under long-term loading gradually extended and may form surface visible damage.Damage could cause the degeneration of cartilage function,make the carrying capacity significant reduce,so the damaged cartilage need to get repair timely. |
